Which are supposed to be the 'ancient bacteria'?

Explanation

**Step-by-Step Solution:**

1. **Identify the Term "Ancient Bacteria":** The term refers to a group of bacteria that are considered to have existed since the early stages of Earth's history.

2. **Name the Group:** The ancient bacteria are known as **Archaea** or **Archaebacteria**.

3. **Reason for Their Classification:** Archaea are considered ancient because they are believed to have originated shortly after the formation of the Earth, making them some of the earliest forms of life.

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